Radiolytic Effects on Fluoride Impurities in a U{sub 3}O{sub 8} Matrix

Abstract

The safe handling and storage of radioactive materials require an understanding of the effects of radiolysis on those materials. Radiolysis may result in the production of gases (e.g., corrosives) or pressures that are deleterious to storage containers. A study has been performed to address these concerns as they relate to the radiolysis of residual fluoride compounds in uranium oxides. The interactions of radiation with crystalline solids, based on the bonding characteristics of the crystal, are described to enhance the understanding of radiolytic effects in uranium oxides. Samples of U02F2wH20 and U~08 (with -1.4 wt YO fluorine content) were irradiated in a 'Co source and in spent nuclear fiel (SNF) elements from the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Container pressures were monitored &roughout the irradiations, and gas and solid samples were analyzed after the irradiations. The irradiation of U02F2~xH20 produced 02-with G(02)-values ranging from 0.007 to 0.03 molecules 02 produced per 100 eV. Neither F2 nor HF was produced by the irradiations. Chemical analysis of solid samples showed that some of the uranium was reduced from U(W) to U(IV). A saturation damage limit for the U02F2SXH20was demonstrated by using the HFIR SNF elements, and the limit was found to be 7-9°/0(at -108 radlh). It is shown that the covalently bonded oxygen is more susceptible to radiation darnage than is the ionically bonded fluorine. Irradiation of U@8 (with -1.4 wt 'XO fluorine content) resulted in neither gas production nor a pressure increase. These experiments led to the conclusion that U@8 is safe during 10ng-tem'Istorage fiOm overpressurization and the production of corrosives caused by gamma radiolysis of residual fluorides.

Water Sorption and Gamma Radiolysis Studies for Uranium Oxides

“…2 This container ( Samples were loaded into the container through the flanged end, either in an inert-atmosphere glove box or in air. The flange was then sealed with an aluminum gasket.…”

“…These samples were either from (1) material produced in the conversion prototype 7 (HFIR-2, HFIR-3) or (2) materials prepared at ORNL for the water sorption studies as described in Sect. 2.1.1 (HFIR-4, HFIR-5, HFIR-6-1, HFIR-6-2, HFIR-6-3).…”

“…Results from the gas analysis of the U 3 O 8 samples are presented in Table 3.3, while those from the gas analysis of the UO 3 •xH 2 O samples are presented in Table 3.4.…”

“…The structure of this apparent dihydrate is actually UO 2 (OH) 2 •H 2 O, which has only one hydrating molecule attached to a dihydroxy uranyl species. 18 The anhydrous form (as prepared) is a orange-colored compound; and, when it forms the hydrated species, the orange compound becomes yellow.…”

“…2 Since a major concern in the development of the 233 U storage standard has involved radiolysis of water that could be associated with the stored oxides, 1 this report documents the study of the gamma radiolysis of water that is sorbed on uranium oxides and compares these results with those from the radiolysis of dry uranium oxides. Furthermore, this study included experiments on the rate and amount of water uptake by uranium oxides, because it was believed that the major cause of radiolytic pressurization was due to the radiolysis of this water.…”